Sometimes when baby kicks one spot a bunch, it gets sore. But I've noticed when s/he is in an awkward position and pushing a head/leg/arm/knee/elbow/butt against the top of my uterus for an extended period of time, it can get really sore, especially to touch. I've noticed if I gently massage the tiny body part (seems like it's usually a head), s/he will re-situate and give me some relief.
I've heard there are certain things you can do to get LO to change positions, but so far the massage thing (and sometimes slightly changing my position) works for me.